Investigations for tuberculosis

Initial investigations for suspected pulmonary tuberculosis (TB) include chest X-ray and sputum microscopy with acid-fast (Ziehl-Neelsen) stain. Sputum culture and susceptibility testing are used to confirm the diagnosis and check for drug resistance.

Children younger than 10 years old with pulmonary TB are rarely able to produce a sputum sample, so early morning gastric aspirates or induced sputum are often used for culture and diagnosis.

Rapid molecular testing (eg nucleic acid amplification testing [eg polymerase chain reaction (PCR)]) for rifampicin resistance is recommended if there is a risk of multidrug-resistant TB (MDR-TB) (see Drug resistance in tuberculosis), and should be performed on all smear-positive sputum samples regardless of risk of multidrug-resistant TB.

The diagnosis of extrapulmonary TB is challenging and requires investigations and sampling directed at the likely affected organ system. It is important to notify radiologists and microbiology laboratory staff that TB is being considered.